1. Field of the Invention
The invention relates to a sputter mask or stencil used to control deposition of material in a physical vapor deposition (PVD) system. More particularly, the invention relates to a method and apparatus for precise formation of features on the surface of a substrate support chuck used in a process chamber.
2. Background of the Related Art
Substrate support chucks are widely used to support substrates within semiconductor processing systems. A particular type of chuck is a ceramic electrostatic chuck that is used in high-temperature semiconductor processing systems such as high-temperature physical vapor deposition (PVD). These chucks are used to retain semiconductor wafers or other work pieces in a stationary position during processing. Such electrostatic chucks contain one or more electrodes embedded within a ceramic chuck body. The ceramic material is typically aluminum-nitride or alumina doped with a metal oxide such as titanium oxide (TiO2) or some other ceramic material with similar resistive properties.
One disadvantage of using a chuck body fabricated from ceramic is that, during manufacture, the support surface is xe2x80x9clappedxe2x80x9d to smooth the ceramic material. Such lapping produces particles that adhere to the support surface. These particles are very difficult to completely remove from the support surface. The lapping process may also fracture the chuck body. Consequently, as the chuck is used, particles are continuously produced by these fractures. Additionally, during wafer processing, the ceramic material can abrade a wafer oxide coating from the underside of the wafer resulting in further introduction of particulate contaminants to the process environment. During use of the chuck, the particles can adhere themselves to the underside of the wafer and be carried to other process chambers or cause defects in circuitry fabrication upon the wafer. It has been found that tens of thousands of contaminant particles can adhere to the backside of a given wafer after retention upon a ceramic electrostatic chuck.
To overcome the disadvantages associated with the workpiece substrate contacting the substrate support chuck, a wafer spacing mask is placed upon the surface of the substrate support chuck. Such a wafer spacing mask is disclosed in commonly assigned U.S. Pat. No. 5,656,093, which is hereby incorporated by reference. The material deposited upon the support surface of the chuck body (i.e., the wafer spacing mask) is a, metal such as titanium, titanium nitride, stainless steel and the like. The material supports a semiconductor wafer in such a way that the surface of the wafer that faces the chuck is spaced apart and substantially parallel to the surface of the chuck. Usually the material is deposited to form a plurality of pads, although any wafer spacing pattern deposited on the surface of the substrate support chuck may be used. Thus, the wafer spacing mask reduces the amount of contaminant particles that adhere to the underside of the wafer.
FIG. 1 depicts a perspective view of a prior art stencil for depositing support surface features. Such stencil is more fully seen and described in U.S. Pat. No. 5,863,396. The above-referenced device is a plate-shaped stencil 100 having a plurality of apertures 108 and a plurality of slots 106 although various other configurations are possible. Material is deposited through the apertures 108 and slots 106 (e.g., via physical vapor deposition) to create the desired surface features on the support surface. The height of such features (i.e., the pads formed by apertures 108) must be within 10% of each other to avoid undue flexing and provide uniform support for the wafer to be processed.
FIG. 2 depicts a cross-section as seen along lines 2xe2x80x942 of FIG. 1 of the prior art stencil as placed on top of a surface 210 of a ceramic electrostatic chuck 200 following deposition of the surface features by physical vapor deposition (PVD). As can be seen, some deposited material 206 forms on the stencil. Some deposited material forms support surface features 204 that have larger dimensions than other features 202. Some features are taller in profile as a result of the xe2x80x9cshadowingxe2x80x9d effect. The xe2x80x9cshadowingxe2x80x9d effect is a condition by which PVD material approaching the stencil at angles that are not nearly perpendicular to the stencil is deposited on the sidewalls of the aperture instead of the support surface. Accordingly, this will cause some features to protrude above a desired height xe2x80x9cdxe2x80x9d from the surface 210. By mapping the inconsistencies in pad height, it has been ascertained that pads over the outer areas of the substrate support are higher than those radially inward. Unfortunately, this condition is undesirable as it leads to non-uniform substrate support, i.e.; the point of contact of the various features with the wafer will be at different heights. A non-uniform substrate support condition alters the critical temperature profile on the wafer and results in excessive bowing of the wafer during chucking. These undesirable conditions eventually alter the quality of the final product.
Therefore, a need exists in the art for a method and apparatus for fabricating a wafer spacing mask having a plurality of features wherein the plurality of features are formed simultaneously, uniform in profile and wherein the wafer spacing mask can easily be removed from the chuck assembly.
The disadvantages heretofore associated with the prior art are overcome by a method and apparatus for forming features on a substrate support chuck. The apparatus is a stencil containing a plurality of apertures, each of said apertures having a dual counterbore. The stencil comprises a plate-shaped one-piece structure having a central opening with a plurality of apertures radiating from the central opening outward about the plate-shaped structure. The stencil is preferably fabricated from a ceramic material such as alumina.
A method of forming features on a surface of a substrate support chuck with the stencil comprises the steps of positioning the stencil on the surface of the substrate support chuck; depositing the material onto the stencil and through a plurality of dual counterbored apertures provided in the stencil to form said features upon the surface of the substrate support chuck; removing said stencil and leaving said features upon said surface of said substrate support chuck. The method uses a stencil having a central opening and a plurality of dual counterbored apertures disposed about the plate.